Devices for measuring the length of yarn spun on each spinning unit are known. When a predetermined length of yarn wound is reached the device sets the spinning unit out of operation by interrupting the sliver supply and, consequently, the spinning process of the spinning unit whose bobbin has been fully wound and is to be replaced by an empty tube. Also known are devices registering the time of an uninterrupted run of each spinning station and cutting off the drive of them after the preselected run interval has elapsed. Then follows the rotor cleaning and afterwards the re-measuring of the preselected run interval, required to keep the quality of produced yarn that depends on the length of the spinning interval. In each of these two cases, the input signal for the electronic control system is represented by a signal indicating that the spinning station in question is running, while the output signal controls, via the electronic control system, an electronic clutch responsible for the supply of the material. In view of the analogy both in function and in use, of these devices, the further description will concern only the version based upon the measuring of the yarn length. The signal indicating the run of a given spinning station arrives from this spinning station at the central electronic system via a two-way bus. The signal controlling the run of the spinning station comes from the central electronic system, passes through the two-way bus, and controls by means of a controlled switch, inserted in the circuit of the electromagnetic clutch, the run of the spinning station in question.
A drawback of such a device consists in the fact that even a temporary failure either of the central system or of the two-way bus can generate a false signal in the circuit of the controlled switches related to the spinning stations and, consequently, yarn ruptures on them resulting in production losses due to the necessity to stop such a spinning station, and also resulting in damage to the yarn quality due to an extra spinning-in spot.